kofoid: mutations in ceratium. 237 



graphical distribution. Do they occur in all seas and at all seasons, or 

 only at certain times of the year or of the life cycle of the organisms, 

 or only in certain localities or under certain conditions 1 Are other 

 species in the genus also produced in the same way 1 Are certain rare 

 and aberrant species produced in this way 1 For example, are Ceratium 

 reflexum and C.paradoxides, which are always found singly, and seem to 

 be structurally ill-adapted to flotation and unable because of their defects 

 ever to establish themselves, — are these defective species continually 

 produced and maintained by repeated mutations'? In what proportion 

 of schizogonies do these sudden changes occur ? What would a complete 

 genealogy of all the descendants from one pair of gametes of Ceratium 

 reveal as to constancy in form 1 



Again we have no conclusive evidence as to the factors which cause or 

 bring about these sudden changes. Are they due to internal phenomena 

 proper to the cell itself, to abrupt changes in ratio of nucleus and cyto- 

 plasm, or in the morphology and functional activity of the chromatin 

 substance, to heterotypical rather than typical mitoses? Or are they 

 due to the shock of modification in external factors such as changes in 

 temperature, salinity, or the chemical composition of the sea water, or to 

 the interaction between these external forces and the substances and 

 processes of the cell 1 



The consequences of these sudden changes in form are also wholly 

 unknown. There is as yet no evidence as to the fate of the newly formed 

 mutants. Do they continue to produce their own kind by schizogony] 

 Do these schizonts conjugate, and are the descendants of the resulting 

 zygote similar to the gametes or to their heteromorphic ancestor 1 ? Do 

 they revert to ancestral types, remain constant, or possibly form other 

 and different species of Ceratium 1 Is there a normal, usual cycle of 

 changes or are such changes sporadic and exceptional 1 



Could an answer be given to any of these queries, much light would be 

 shed upon the meaning of this phenomenon, its relation to life processes 

 of the organism, and its significance for the theories as to the origin of 

 species and the process of evolution in general. 



Four different interpretations may be given to the phenomenon. 



Seasonal Polymorphism (Gran and Lohmann). 

 These changes are seasonal, temporal variations. This is the interpreta- 

 tion of Lohmann (1908), who has followed in the main the conclusions of 

 Gran (1904) regarding a similar phenomenon in diatoms. He regards 

 the heteromorphic schizonts, the anterior members of his chain (see figs. 



